Scheduling And Sequencing Flashcards
(24 cards)
What is scheduling?
A term used in operations planning and control to indicate the detailed timetable of what work should be done, when it should be done and where it should be done.
What is the definition of routing?
The operations to be performed, their sequence, the work centres, and the time standards
What is the definition of bottleneck?
A resource whose capacity is less than the demand placed on it
What is the definition of queue
A waiting line
What is the definition of due date?
When the job is supposed to be finished
What is the definition of slack?
The time that a job can be delayed and still finish by its due date
Scheduling operations
- companies differentiate based on product volume and product variety
- differentiation affects how the company organises its operations
- each kind of company operation needs different techniques (High/Low volume operations
What are high volume operations
Also called flow operations, can be repetitive (e.g production of automobiles, bread) or continuous (e.g, production of crude oil, water treatment)
Details of high volume operations
- high volume standard items; discrete or continuous with smaller profit margins
- designed for high effiency and high utilisation
-high volume flow operations with fixed routings - bottlenecks are easily identified
- commonly uses line balancing to design the process around required tasks
What are low volume operations?
Low volume operations, also called job shop operations, are designed for flexibility
Details of low volume operations
- use more general purpose equipment
- Customised products with higher margins
- each product or service may have its own routing (scheduling is much more difficult)
- bottlenecks move around depending upon products being produced at any given time
What are the 2 types of scheduling techniques?
- forward scheduling
- backward scheduling
What are the 2 types of scheduling techniques?
- Forward scheduling
- Backward scheduling
What is forward scheduling?
Starts processing immediately when a job is received (regardless of due date)
(If jobs are finished before due date this can lead to a build up of inventory)
What is backward scheduling?
Begin scheduling the jobs last activity so that the job is finished on due date
(Shows how late the job can be started and still be on time)
How do you sequence jobs?
- which of several jobs should be scheduled first?
- techniques are available to do short term planning of jobs based on capacity and priorities
ALSO USE PRIORITY RULES
What are priority rules?
- decision rules to allocate the relative priority of jobs at a work centre
- local priority rules: determines priority based on only jobs at an individual workstation
- global priority rules: also considers all the remaining workstations a job must pass through
Commonly used priority rules
- first come, first served (FCFS)
- last come, first served (LCFS)
- earliest due date (EDD)
- shortest processing time (SPT)
- longest processing time (LPT)
- slack per remaining operations (S/RO)
(Slack / number of remaining operations)
How do you use priority rules?
- Decide which priority to use
- List all jobs waiting to be processed with their job time
- Using a priority rule, determine which job has highest priority then 2nd, 3rd and so on
Measuring scheduling performance
(Job flow time + calculation mean flow time)
Job flow time - time a job is completed minus the time the job was first available for processing; avg flow time measures responsiveness
Calculation mean flow time - MFT = (sum job flow times)/ # of jobs (includes wait time, set up time, processing time and delays)
= (10+13+17+20)/4 = 60/4 = 15 days
Measuring scheduling performance
(Average # jobs in system + calculating average number of jobs in system)
Average # jobs in system - measures amount of work in progress; avg # measures responsiveness and work in process inventory
Calculating average number of jobs in the system - average # jobs = (sum job flows) / # days to complete batch
= (10+13+17+20)/20 = 3 jobs
= (60)/20 = 3 jobs
Scheduling performance calculations
(Makespan + makespan is the length of time to complete a batch)
Makespan - the time it takes to finish a batch of jobs; measure of efficiency (20 days)
Makespan is the length of time to complete a batch - Makespan = completion time for job D minus start time for job A
= 20-0= 20 days
Job lateness + job tardiness
Job lateness - whether the job is completed ahead of, on, or behind schedule
Job tardiness - how long after the due date a job was completed, measures date performance
Both are measures related to customer service
Scheduling for service organisations
(Demand management + managing service capacity)
Demand management - appointments and reservations, posted availability, delayed services or backlogs (queues)
Managing service capacity - staff for peak demand (if cost is not prohibitive), floating employees or employees on call, temporary season or part time employees
